Flame shield for electric vehicle battery and battery housing including flame shield

Abstract

In a primary aspect, the present invention relates to a flame shield for electric vehicle batteries, particularly lithium-ion batteries, and to a method for manufacturing the flame shield. The flame shield according to the present invention comprises at least one flame-resistant layer made of a porous fibrous nonwoven fabric impregnated with polyurethane, wherein the melting temperature of the fibers contained within the porous fibrous nonwoven fabric is at least 1100°C, the polyurethane does not contain any flame retardants, and the polyurethane has impregnated the porous fibrous nonwoven fabric such that the flame-resistant layer is impermeable to airflow. In a second aspect, the present invention relates to a battery housing, wherein the battery lid and / or battery tray comprises such a flame shield.

Description

[Technical Field]

[0001] The present invention relates to a flame shield for an electric vehicle battery and a method for manufacturing the flame shield, and further to a battery housing including such a flame shield. [Background technology]

[0002] Electric vehicles are typically powered by rechargeable batteries that provide the electrical power needed to drive the electric motors used to propel the vehicle. The batteries typically consist of a number of electrically connected battery cells, sometimes organized into battery modules.

[0003] Among the different types of rechargeable batteries, lithium-ion batteries are used in electric vehicles in particular due to their high energy density, which can ensure a longer driving range for a given battery weight.

[0004] In electric vehicles, batteries are usually mounted in the area under the vehicle body. Typically, the batteries are enclosed inside a battery case, which consists of a lower shell on which the batteries are placed, hereinafter referred to as the battery tray, and an upper shell, hereinafter referred to as the battery cover or battery lid, which encloses the batteries from above. Typically, the battery case, and in particular the battery cover, is made of a metallic material. Aluminum is very commonly used for this purpose due to its favorable stiffness / weight ratio.

[0005] In some cases, the battery may be sealed between the body floor and a battery tray that is fixed directly to the body and that the battery rests on. In these cases, it is the body floor, typically made of aluminum or steel, that acts as the battery cover.

[0006] Rechargeable batteries for electric vehicle traction, specifically lithium-ion batteries, can pose significant safety concerns. Mechanical abuse (e.g., impact, puncture), and / or thermal abuse (e.g., overheating), and / or electrical abuse (overcharging) can result in a short circuit within one or more battery cells. A short circuit can cause exothermic decomposition of the battery cell's chemical components. This can significantly increase the battery cell's temperature, which can then propagate to nearby battery cells, causing them to overheat and potentially creating a cascading effect known as thermal runaway.

[0007] During thermal runaway, extremely high temperatures can develop inside the battery in a very short time, causing the battery cell's chemical components to ignite and, ultimately, in extreme cases, even explode. Specifically, thermal runaway in lithium-ion batteries can produce flames with temperatures up to approximately 900°C. These temperatures are well above the melting point of typical battery covers and / or vehicle floor panels, which are made of, for example, aluminum.

[0008] Furthermore, as a battery ages, its susceptibility to thermal and electrical abuse increases, and this increases the risk of thermal runaway.

[0009] In the event of thermal runaway, it is first and foremost important to warn occupants early enough to leave the vehicle cabin before unbearable temperatures and / or flames reach the cabin, so as not to endanger the safety of the occupants therein. To this end, Chinese Standard GB 38031-2020 requires that the battery management system provide a warning signal at least five minutes (the so-called "time-to-escape") before heat propagation due to a thermal runaway event (even a single battery cell event) occurs. In addition, to further protect the vehicle cabin from high temperatures and / or flames during the aforementioned "escape time," protective flame shields are typically applied on the battery cover and / or on the body floor panels, generally on the side facing the battery.

[0010] Prior art flame shields typically consist of a thin mica layer, which is applied to the battery-facing side of the battery cover and / or body floor panel. Indeed, mica is a highly effective flame shielding material, with a melting temperature of approximately 1300°C. However, mica-based flame shields present several problems.

[0011] Mica is a fairly heavy material, with a density of 2700 kg / m 3 ~3000kg / m 3 Therefore, flame barriers containing mica layers can be quite heavy, with area weights ranging from 2.5 kg / m² depending on the thickness of the mica layer. 2 ~6kg / m 2 Such area weight can be even greater than the area weight of the battery cover to which the flame shield is applied. This has a significant negative impact on the driving range of the electric vehicle, which is a very important feature for end consumers interested in this type of vehicle.

[0012] Additionally, the overall manufacturing process for mica flame barriers is extremely time-consuming and industrially complex. This process begins with the mining of mica, which must then be sorted, purified to remove all contaminants, and converted into mica paper. Mica paper consists of extremely thin layers of mica flakes, held together only by weak van der Waals forces. This extremely delicate structure of mica paper makes its manufacture difficult and highly dependent on critical parameters, such as the chemical pulping composition, mica distribution, and its areal weight. (The critical dependence of the mica paper manufacturing process on these parameters can be reflected in the heterogeneity of the resulting mica paper.) From an industrial perspective, a manufacturing process that is simpler in terms of material procurement and manufacturing steps, and less critical in terms of process parameter definition, is highly desirable.

[0013] Furthermore, flame shields including mica layers can be difficult to form into strong, three-dimensional shapes. This is due to the fragility of mica, which relies on a microscopic structure based on a layered crystal lattice, in which octahedral aluminum layers alternate with tetrahedral silicon oxide layers. Due to this microscopic structure, mica has a natural tendency to fracture, i.e., break primarily along crystallographic lines or planes, and cannot be easily formed along strong curvatures. This can be problematic when a flame shield including a mica layer must be applied to a battery cover (or vehicle body) that exhibits areas with strong three-dimensional curvature and may not even allow the flame shield to be applied in such areas, potentially compromising the performance of the flame shield and compromising the safety of occupants in the vehicle cabin. Summary of the Invention [Problem to be solved by the invention]

[0014] It is an object of the present invention to provide a flame shield for electric vehicle batteries that provides an alternative solution to the prior art mica layers and overcomes the weight, manufacturing process, and performance issues mentioned above. [Means for solving the problem]

[0015] The object of the present invention is achieved by a flame shield for a battery of an electric vehicle according to claim 1, a method for producing such a flame shield according to claim 13, and a battery housing comprising such a flame shield according to claim 14.

[0016] In a main aspect, the present invention relates to a flame shield for electric vehicle batteries, in particular lithium-ion batteries, comprising at least one flame resistant layer made of a porous fibrous nonwoven fabric impregnated with polyurethane, wherein the melting temperature of the fibers contained within the porous fibrous nonwoven fabric is at least 1100°C, the polyurethane does not contain any flame retardants, and the polyurethane has impregnated the porous fibrous nonwoven fabric such that the flame resistant layer is impermeable to airflow. [Effects of the Invention]

[0017] Hereinafter, an electric vehicle is any vehicle that is powered solely or partially by a battery, including, but not limited to, fully electric vehicles, hybrid vehicles, plug-in hybrid vehicles, and vehicles with range extenders.

[0018] A "layer" is a body made of one or more materials and filling the space between two closely spaced surfaces. The spacing between the surfaces is much smaller than their size. The two surfaces are referred to as sides of the layer, and they face each other. The spacing between the two surfaces is called the thickness of the layer. This thickness may vary. A layer may contain other layers.

[0019] An airflow impermeable layer is one that has an airflow impermeability of 0.02 l / sm at a pressure difference of 75 Pa when tested in accordance with ASTM E 2178 or E 283. 2 This means a layer having the following air permeability:

[0020] A "fibrous nonwoven" is a random network of fibers bonded together by chemical, mechanical, thermal, or solvent treatment. A "porous fibrous nonwoven" is a fibrous nonwoven in which gaps exist between the fibers. These gaps are hereafter referred to as "pores."

[0021] It has been found, quite surprisingly, that simply impregnating a porous fibrous nonwoven fabric with polyurethane can provide an effective flame-resistant layer suitable for use in a flame shield for an electric vehicle battery to mitigate the consequences of thermal runaway and protect the vehicle interior during evacuation. However, it has been found that to achieve the desired flame-resistant effect, the fibers contained within the porous fibrous nonwoven fabric must be resistant to high temperatures, specifically, the melting temperature of the fibers must be above 1100°C, and the polyurethane must be impregnated into the porous fibrous nonwoven fabric in a manner that renders the resulting composite impermeable to airflow. Even more surprisingly, it has been found that the flame-resistant effect can be achieved without adding any flame retardants to the polyurethane.

[0022] In the simplest embodiment, the flame shield according to the invention may consist of only one flame-resistant layer according to the invention. In another embodiment, the flame shield according to the invention may consist of two or more flame-resistant layers according to the invention, which partially or completely overlap each other. It is noteworthy that in these embodiments, the flame shield according to the invention is significantly simpler in terms of raw materials, material procurement, and manufacturing processes compared to prior art solutions based on mica layers.

[0023] In more complex embodiments, the flame barrier according to the invention may also comprise complementary layers, i.e. layers different from the flame-resistant layer according to the invention. Such layers may be included in the flame barrier according to the invention in order to further improve the flame-blocking properties of the flame barrier and / or for other purposes, for example to improve the mechanical properties and / or to improve the processability during manufacturing or installation and / or to improve the appearance.

[0024] Polyurethanes according to the present invention are typically obtained from the reaction of a polyurethane-forming mixture containing a polyol and an isocyanate. The polyol and isocyanate may be premixed immediately prior to deposition. The polyurethane-forming mixture generally used in the process of the present invention includes at least one polyol component having an average OH number of 300 to 900, with individual polyols having a functionality of 2 to 6; at least one isocyanate, preferably methylene diphenyl diisocyanate (MDI), polymeric MDI, or at least one isomeric blend of prepolymers thereof; optionally, a blowing agent, preferably water, one or more catalysts, including amine-based and metal-based catalysts; a surfactant or stabilizer; a mold release agent; and additives, such as fillers, colorants, or rheology modifiers. Suitable polyols may be polyester-based or polyether-based.

[0025] US808485 discloses preferred mixtures comprising an isocyanate component and a polyol component comprising one or more natural oil-based polyols, which may be used with the present invention. Other renewable resources, such as starch, lignin, cellulose, or recycled polyester polyols, may also be used.

[0026] The porous fibrous nonwoven fabric may be in any form known to those skilled in the art. Preferably, the weight of the porous fibrous nonwoven fabric is 40% to 80%, preferably 50% to 70%, of the total weight of the flame-resistant layer according to the present invention.

[0027] In a preferred embodiment, the porous fibrous nonwoven fabric according to the present invention may comprise one or more porous fibrous layers that wholly or partially overlap each other, each of which may be in any form known to those skilled in the art, including, for example, a chopped strand mat, a knit, a woven fabric, or a non-crimp fabric.

[0028] The porous fibrous nonwoven fabric according to the present invention may be obtained using any method for producing porous fibrous layers known to those skilled in the art, which may include process steps such as carding, spunbonding, meltblowing, electrospinning, wrapping (e.g., vertical wrapping, cross wrapping), needle punching, air laying, or wet laying, or any combination thereof.

[0029] In a preferred embodiment, the porous fibrous nonwoven fabric comprises at least one fibrous layer, the fibers of which are bonded by a thermosetting binder. The thermosetting binder is preferably a phenolic or epoxy binder. The fibrous layer may comprise staple fibers or continuous filaments or a combination of both. The purpose of the binder is to hold the fibers together so that the fibrous layer can be properly handled and transported during the manufacture of the flame shield according to the invention.

[0030] It is worth noting that the process used for the porous fibrous nonwoven fabric according to the invention, as well as its form, only has a small effect on the effectiveness of the flame-resistant layer according to the invention. This makes the industrial production of the flame barrier according to the invention easier, particularly in terms of material procurement. If the melting point of the fibers contained in the porous fibrous nonwoven fabric is at least 1100°C and the fibrous nonwoven fabric is completely impregnated with polyurethane so that it is air-impermeable, a flame-resistant layer with excellent flame-resistant properties is obtained.

[0031] These excellent flame-blocking properties are surprisingly achieved through a synergistic effect between the high-temperature resistance of the fibers contained within the porous fibrous nonwoven fabric and the impregnation of the porous fibrous nonwoven fabric with the polyurethane according to the present invention. On the one hand, the fibers, in addition to providing dimensional stability to the flame-resistant layer according to the present invention, can also transfer heat, distribute it over the entire surface of the layer, and act as an effective heat storage medium. On the other hand, the polyurethane completely impregnates the fibrous nonwoven fabric, making the flame-resistant layer impermeable to airflow and thereby preventing flame propagation through the layer. Furthermore, by adhering to the fibrous fabric, the polyurethane does not drip when melted under the action of a flame, but rapidly carbonizes, forming char deposits around the fibers and on the surface of the layer, which acts as an additional heat storage medium.

[0032] To achieve this effect, it is essential that the polyurethane completely impregnates the porous fibrous nonwoven fabric, i.e., that the fibrous nonwoven fabric is immersed in the polyurethane so that the polyurethane fills all the pores of the fibrous nonwoven fabric and tightly surrounds all the fibers contained within the fibrous nonwoven fabric, so as to make the porous fibrous nonwoven fabric impermeable to airflow.

[0033] In a preferred embodiment, the polyurethane-forming mixture does not contain any blowing agent. The absence of a blowing agent prevents the polyurethane impregnating the porous fibrous nonwoven fabric from forming a foam, thereby minimizing or eliminating the presence of air bubbles in the polyurethane. Such air bubbles can adversely affect the performance of the flame-resistant layer according to the present invention, because they facilitate the propagation of flames through the layer. By preventing the polyurethane from forming a foam, improved flame-blocking properties of the porous fibrous layer according to the present invention are thus obtained.

[0034] Furthermore, the surprising effect described above makes it possible to obtain excellent flame-blocking properties using polyurethanes that do not contain any flame retardants. This is certainly extremely advantageous. First of all, it generally makes the flame-blocking body according to the invention cheaper and easier to manufacture industrially. Secondly, it makes it possible to avoid all the undesirable side effects of flame retardants commonly used in commercial polyurethanes, whether they are additive flame retardants (i.e., flame retardants that are not chemically bound to the polyurethane polymer) or reactive flame retardants (i.e., flame retardants that are chemically bound to the polyol used in the polyurethane-forming mixture).

[0035] Indeed, reactive flame retardants, such as halogen- and / or phosphorus-containing polyols, can pose toxicity / occupational hygiene problems, and the same applies to some additive flame retardants, such as TCPP (tris(1-chloro-2-propyl)phosphate) or TEP (triethylphosphate).

[0036] Furthermore, other additive flame retardants typically used in commercial polyurethanes, such as expandable graphite or ammonium phosphate, have the property of expanding, i.e., they expand under heat. This property makes them unsuitable for use in flame shields to be applied to the battery side of the battery cover and / or battery tray of an electric vehicle because, by expanding, the flame retardant additives can reduce or even fill the gap between the battery cover and / or battery tray and the battery cell, thus creating a dangerous short circuit between these elements.

[0037] All the above shows that the flame resistant layer according to the invention can offer considerable advantages by avoiding the use of flame retardants, whilst surprisingly retaining excellent flame blocking properties.

[0038] The flame-resistant properties and performance of the flame-resistant layer according to the present invention are preferably tested as follows. The flame source used for the test is a Bunsen burner equipped with a gas valve for adjusting the gas supply and a controller for adjusting the air volume. The burner tube must have an inner diameter of (9.5±1.5) mm and a length of (90±6) mm, without any flame stabilizers at the end of the tube. Commercially available propane or equivalent gas is used as fuel. Before the test begins, the flame is adjusted so that the flame temperature at the tip and center of the flame is (1000±100)°C. The flame temperature at the tip of the flame is measured at a distance of 57 mm from the end of the burner tube, while the flame temperature at the center of the flame is measured at a distance of 35 mm from the end of the burner tube. Temperatures can be measured using a digital thermometer or any suitable device, such as a pyrometer or thermocouple. A square, flat specimen of the flame-resistant layer measuring 250 mm to 350 mm is prepared and fixed in a horizontal position in a specimen holder. The specimen holder may consist, for example, of a metal frame. The specimen is clamped within the metal frame along its perimeter. The area of ​​the specimen left exposed (i.e., not covered by the frame) must have a square with a side measuring at least 200 mm. The specimen is exposed to the Bunsen burner flame from one side (commonly referred to as the "flame side") for a predetermined time by positioning the specimen horizontally 60 mm from the end of the Bunsen burner. The end of the tube must be aligned with the center of the specimen. During the test, the flame temperature at the center of the flame is measured and checked to ensure it remains equal to (1000 ± 100) °C. Additionally, the temperature of the specimen at the center of the side opposite the side exposed to the flame (commonly referred to as the cover side) is also measured during the test using one of the measuring devices described above (e.g., a digital thermometer or thermocouple). The difference between the temperature at the center of the flame and the temperature at the center of the specimen on the cover side is hereafter referred to as the "temperature drop" across the specimen. The greater the temperature drop, the better the performance of the flame resistant layer.

[0039] The preferred test procedure described above is hereinafter referred to as the "Bunsen burner" test. This type of test procedure can be advantageous because it allows for testing the flame-blocking properties of flame shields to be used for electric vehicle batteries on relatively small test specimens and with limited laboratory space and resources, thus avoiding the need to perform expensive and costly testing on the entire flame shield or the entire battery cover equipped with the flame shield.

[0040] Preferably, the duration of the Bunsen burner test is at least 5 minutes, more preferably at least 10 minutes, and even more preferably 15 minutes.

[0041] In order to improve the protection guaranteed by the flame shield according to the invention during the escape time, the temperature drop across the flame resistant layer according to the invention, measured in a Bunsen burner test, is preferably at least 350° C., more preferably at least 500° C., and even more preferably at least 600° C. This means that such a temperature drop is maintained for the entire duration of the test.

[0042] The fibers contained within the porous fibrous nonwoven fabric according to the invention must be resistant to high temperatures, in particular their melting temperature must be at least 1100° C. To further enhance the flame protection capability, the fibers contained within the porous fibrous nonwoven fabric according to the invention are preferably able to withstand temperatures of up to 1100° C. for at least 5 minutes, preferably at least 10 minutes, and even more preferably at least 15 minutes without burning and / or dripping.

[0043] According to one embodiment of the present invention, the porous fibrous nonwoven fabric of the present invention may comprise one or more porous fibrous layers containing staple fibers. Staple fibers are fibers cut to a specified length, unlike endless filaments, which are continuous fibers with an unlimited length. The length of the staple fibers contained in the porous fibrous nonwoven fabric of the present invention is preferably 20 mm to 80 mm, more preferably 30 mm to 70 mm, and even more preferably 40 mm to 60 mm.

[0044] In a preferred embodiment of the present invention, the porous fibrous nonwoven fabric according to the present invention may comprise one or more layers containing fibers in the form of endless filaments. Endless filaments, hereinafter also referred to as "continuous filaments" or simply "filaments," are continuous fibers that have an unlimited length, i.e., are not cut to a specific length like staple fibers. Endless filaments allow for a more homogeneous distribution of fibers across the surface of the layer, particularly when the flame-resistant layer has a substantially non-planar shape with regions of strong three-dimensional curvature.

[0045] Additionally, when the porous fibrous nonwoven fabric according to the present invention comprises one or more layers containing endless filaments, the mechanical strength and rigidity of the flame-resistant layer according to the present invention can be improved, specifically in terms of bending rigidity and bending strength. These improved mechanical properties result from the synergistic interaction between the endless nature of the filaments and the inter-filament bonding ensured by the polyurethane impregnating the filaments. In fact, on the one hand, the endless filaments extend over the entire surface of the flame-resistant layer. On the other hand, the polyurethane ensures a uniformly distributed bond between the endless filaments along the entire length of the filaments themselves. This results in a network of endless filaments that extend over the entire surface of the flame-resistant layer and are strongly connected to each other. This network has excellent mechanical properties, specifically in terms of bending rigidity and bending strength.

[0046] The porous fibrous nonwoven fabric according to the present invention may comprise one or more fibrous layers comprising inorganic fibers made from inorganic materials, such as glass fibers, carbon fibers, basalt fibers, aramid fibers, or mixtures thereof. Preferably, the fibrous layers comprised within the porous fibrous nonwoven fabric comprising inorganic fibers comprise at least 70% by weight, more preferably at least 80% by weight, and even more preferably at least 90% by weight of inorganic fibers.

[0047] In a preferred embodiment, the porous fibrous nonwoven fabric according to the present invention comprises one or more layers containing E-glass fibers, which may partially or completely overlap one another. E-glass fibers can resist thermal expansion, which can provide dimensional stability to the layers in the presence of temperature fluctuations that may occur throughout the battery's operating life. E-glass fibers can also provide high mechanical strength and stiffness at a low weight, which can simultaneously exhibit low values ​​for dielectric constant, dielectric loss, or both. E-glass fibers may comprise any of silica, alumina, calcium oxide, and boron oxide.

[0048] In a further preferred embodiment, the E-glass fiber may be free of boron oxide. Such boron-free materials are referred to as E-CR glass. E-CR glass can provide acid and / or chemical resistance. E-CR glass can also provide improved temperature resistance.

[0049] The layers containing E-glass and / or E-CR glass fibers may be formed by any suitable process known to those skilled in the art, including, by way of example only, needle punching, air laying, or wet laying.

[0050] In a particularly preferred embodiment, the fibrous nonwoven fabric comprises one or more E-glass fiber layers, each layer in the form of a chopped strand mat of E-glass staple fibers bound together by a small amount of a thermosetting binder, preferably 10% by weight, more preferably 5% by weight. The thermosetting binder is preferably a phenolic or epoxy polyester resin. In this embodiment, the length of the E-glass staple fibers is preferably 20 mm to 80 mm, more preferably 30 mm to 70 mm, and even more preferably 40 mm to 60 mm.

[0051] In another preferred embodiment, the porous fibrous nonwoven fabric according to the present invention may include one or more layers consisting essentially of a ceramic fiber blanket (hereinafter referred to as the "ceramic blanket"). The ceramic blanket layer may provide improved handling strength, enhanced thermal properties, or both. The ceramic blanket layer may have excellent thermal stability, good flexibility, ease of cutting and forming. The ceramic blanket may also have good tear resistance. The ceramic blanket layer may be formed by any suitable process, including, by way of example, needle punching.

[0052] The ceramic blanket may contain little to no binder (e.g., about 1% or less by weight of the layer). The ceramic blanket may be formed from inorganic materials in an amount up to about 100% by weight, including about 100% by weight of the layer. For example, the ceramic blanket may contain silicon dioxide, calcium oxide, and magnesium oxide.

[0053] The porous fibrous nonwoven fabric according to the present invention may include one or more fiberglass layers, which can provide the flame resistant layer according to the present invention with high temperature resistance and thermal stability, abrasion resistance, tear resistance, and chemical solvent resistance.

[0054] The fibrous nonwoven fabric may include one or more layers containing organic fibers. The layer containing organic fibers preferably contains at least 50% by weight of organic fibers, more preferably at least 75% by weight of organic fibers. In a preferred embodiment, the fibers may be formed from or contain an organic synthetic thermoplastic polymer resin. For example, the fibers may be polyacrylonitrile fibers. The polyacrylonitrile fibers may be oxidized polyacrylonitrile fibers, such as Ox-PAN, OPAN, or PANOX.

[0055] The fibers contained within the porous fibrous nonwoven fabric according to the present invention may be virgin and / or originate from a recycling process, which may be a post-industrial recycling process or a post-consumer recycling process.

[0056] For example, the glass fibers contained in the porous fibrous nonwoven fabric according to the present invention may originate from the end-of-life treatment of GFRP (Glass Fiber Reinforced Polymer) products, such as aircraft and ship body panels, by thermal (fluidized bed processing) and / or chemical treatment. These treatments allow the glass fibers to be separated from the polymer matrix and recycled. In another embodiment, the glass fibers contained in the porous fibrous nonwoven fabric according to the present invention may be produced from post-industrial glass waste.

[0057] Quite surprisingly, the desired flame-blocking effect can already be obtained with a very thin and lightweight flame-resistant layer. The density of the flame-resistant layer according to the invention is preferably 800 kg / m 3 ~1800kg / m 3 and more preferably 1000 kg / m 3 ~1500kg / m 3These density values ​​are significantly lower than the density of mica, a material commonly used by those skilled in the art for flame shields for batteries in electric vehicles. Compared to prior art flame shields, the flame shield according to the invention thus allows a reduction in the weight of the electric vehicle and, as a consequence, also an improvement in the range of the electric vehicle, a feature highly desired by end consumers interested in this type of vehicle.

[0058] Preferably, the thickness of the flame-resistant layer according to the present invention is 0.5 mm to 7 mm, more preferably 0.5 mm to 5 mm, and even more preferably 1 mm to 3 mm. Thus, the flame shield according to the present invention can be realized at the cost of almost negligible packaging space. This can be particularly advantageous considering the very limited space typically available inside a battery case enclosing a battery for an electric vehicle, specifically the space between the battery cover and the battery cell where the flame shield can be positioned.

[0059] The flame shield according to the present invention may be manufactured by methods known to those skilled in the art. A preferred manufacturing process comprises the following steps: 1. A porous fibrous nonwoven fabric is provided, and the melting temperature of the fibers contained in the fibrous nonwoven fabric is at least 1100°C; 2. Spreading a polyurethane-forming mixture that does not contain any flame retardants onto the porous fibrous nonwoven fabric. Following mixing of the polyol component and the isocyanate component, the resulting polyurethane-forming mixture is typically in the form of a viscous fluid that can be easily poured onto the porous fibrous nonwoven fabric, for example, through a mixing head. The polyurethane-forming mixture may be mixed and metered just before spreading it onto the porous fibrous nonwoven fabric. Additives may be added to the polyol component or the isocyanate component before or during the mixing stage; 3. The porous fibrous nonwoven fabric obtained in the second step, on which the polyurethane-forming mixture has been spread, is transferred into a mold heated at a temperature of 40°C to 200°C, and the cavity of the mold has a shape desired for the flame shield; 4. closing the mold and hot pressing the transferred material stack into the heated mold by keeping the mold closed under pressure with a clamping force of 100-2000 tons, the heat of the mold (further) activating the polyurethane mixture and creating pressure that causes the polyurethane to spread around the fibers and through the pores of the porous fibrous nonwoven fabric, thereby impregnating the porous fibrous nonwoven fabric; 5. Demoulding and optionally trimming the edges; Go through the process.

[0060] In a variation of the above process, spreading the polyurethane-forming mixture onto the porous fibrous nonwoven fabric may be carried out directly in a heated mold, which may be advantageous as it may reduce the space and time required to produce the flame shield according to the invention.

[0061] As already mentioned, this process is extremely simple compared to the processes required to produce prior art flame shields based on mica layers. The above-described process results in a flame shield according to the invention consisting of only one flame-resistant layer. Quite obviously, this process can be extended to cases in which the flame shield according to the invention comprises two or more flame-resistant layers.

[0062] It is noteworthy that the above process can produce a flame-resistant layer having a three-dimensional shape, i.e., a shape that substantially deviates from a planar shape. This design flexibility is a result of the flame-resistant layer components, i.e., porous fibrous nonwoven fabric and polyurethane, both of which have high moldability. This is advantageous compared to prior art flame shields based on mica layers. In the case of using a mica layer, the fragility of the mica may prevent it from conforming to the shape of a battery cover with a strong curvature.

[0063] A further aspect of the present invention relates to a battery housing or battery case for an electric vehicle battery, in particular a lithium-ion battery, comprising a battery cover and a battery tray, wherein a flame shield according to the present invention is disposed on the battery cover and / or on the battery tray on the side facing the battery.

[0064] The design flexibility of the flame shield according to the invention allows it to follow the shape of the battery cover and / or battery tray even in areas where this shape is far from planar, for example in areas where this shape exhibits strong curvatures and / or features such as beads, embossments, etc. This can be advantageous for maximizing the coverage and thus the effectiveness of the flame shield according to the invention.

[0065] The coverage of a flame shield is the ratio of the area of ​​the side of the battery cover / tray facing the battery that is covered by the flame shield to the total area of ​​that same side, hereinafter expressed as a percentage.

[0066] Furthermore, in the battery housing according to the present invention, the flame shield according to the present invention may be applied on the battery cover and / or on the battery tray in the form of a single piece or in the form of a patch, depending on the design needs.

[0067] Preferably, in order to improve the flame-blocking properties of the flame barrier according to the invention, the coverage of the flame barrier according to the invention is at least 50%, more preferably at least 60%, even more preferably at least 70%.

[0068] Any range given throughout this specification is intended to include the starting and endpoints, as well as the normal expected deviations in measurements. The starting and endpoint values ​​of the various ranges can be combined.

[0069] Further embodiments of the invention can be derived from the description also by combining different embodiments and examples of the invention and also from the description of the embodiments shown in the drawings, which are schematic and not necessarily drawn to scale. [Brief explanation of the drawings]

[0070] [Figure 1] 1a and 1b show a flame shield according to the present invention. [Figure 2] FIG. 2 illustrates a typical process that can be used to make this. [Figure 3] FIG. 3 is a diagram showing an outline of the Bunsen burner test. [Figure 4] FIG. 4 is a diagram showing a battery case according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0071] Figures 1a and 1b show a flame barrier (1) according to the present invention in its simplest embodiment. The flame barrier consists of a substantially flat flame-resistant layer (3) made of a porous fibrous nonwoven fabric completely impregnated with a polyurethane (2) according to the present invention. Figure 1a shows a top view of the flame barrier, while Figure 1b shows a representative cross section. As can be seen in these figures, the polyurethane completely surrounds the fibers of the porous fibrous nonwoven fabric and fills its pores, making the flame-resistant layer impermeable to airflow. Preferably, no fiber ends protrude beyond the surface facing at least a potential flame source.

[0072] Figure 2 shows a schematic representation of the main steps of a preferred manufacturing process for a flame shield according to the present invention. These steps include: In a first step (100), a porous fibrous nonwoven fabric (3) is prepared, - In a second step (200), the polyurethane-forming mixture, which does not contain any flame retardant, is spread onto the porous fibrous nonwoven fabric (3) by means of one or more polyurethane mixheads (10), which are capable of moving relative to the porous fibrous nonwoven fabric (3) and the surface (11) onto which the mixture has to be poured. The polyurethane mixture may be mixed and metered just before spraying, for example using a first metering system for the isocyanate (12) and a second metering system for the polyol (13) in the mixing unit (14). Additives may be added to the mass or directly to the mixing unit; - in a third step (300), the porous fibrous nonwoven fabric (15) on which the polyurethane-forming mixture has been spread is transferred into a mold (16) heated at a temperature between 40°C and 200°C, the mold comprising first and second mold halves (16a) and (16b), which are closed together to form a cavity therebetween having a shape desired for the flame shield; - In a fourth step (400), the mold is closed and kept closed under pressure to form the part (17). The heat of the mold (further) activates the polyurethane-forming mixture, creating a foam pressure that helps the mixture to impregnate the porous fibrous nonwoven fabric, spreading the mixture around the fibers and through the pores of the porous fibrous nonwoven fabric. - In a fifth step (500), the final part (17) is released from the tool and optionally trimmed. The reason is that.

[0073] Five different flame shields according to the present invention, and more specifically according to the embodiment shown in FIG. 1, were manufactured according to the process outlined in FIG.

[0074] The first flame barrier according to the present invention consists of a single flame-resistant layer, with an area weight of 450 g / m2, impregnated with a polyurethane obtained by a polyurethane-forming mixture containing a polyol component with an average OH number of approximately 700 and MDI isocyanate. 2The melting temperature of the glass fibers contained in the E-glass fiber chopped strand mat used for the first flame-resistant layer according to the present invention is about 1135°C. The polyurethane does not contain any flame retardants. The resulting flame barrier is only 0.8 mm thick and has a density of 1036 kg / m 3 and the area weight is approximately 830 g / m 2 The size of the flame barrier was approximately 300mm x 300mm.

[0075] The second flame barrier according to the invention is obtained in the same way as the first flame barrier according to the invention, with the only difference being that the porous fibrous nonwoven fabric has a density of approximately 900 g / m 2 The fact is that it consists of two overlapping E-glass fibre chopped strand mats with a total area weight of 1.4 mm. The resulting flame barrier has a thickness of 1.4 mm and a density of 1158 kg / m 3 and the area weight is approximately 1620 g / m 2 is.

[0076] The third flame barrier according to the invention is obtained in the same way as the first flame barrier according to the invention, with the only difference being that the porous fibrous nonwoven fabric has a density of approximately 1350 g / m 2 The fact is that it is made of three overlapping E-glass fibre chopped strand mats with a total area weight of 1.6 mm. The resulting flame barrier has a thickness of 1.6 mm and a density of 1393 kg / m 3 and the area weight is approximately 2230 g / m 2 is.

[0077] The fourth flame barrier according to the invention is obtained in the same way as the first flame barrier according to the invention, with the only difference being that the porous fibrous nonwoven fabric has a density of approximately 1800 g / m 2 The fact that it is made of four overlapping E-glass fibre chopped strand mats has a total area weight of 1.8 mm. The resulting flame barrier has a thickness of 1.8 mm and a density of 1520 kg / m 3 and the area weight is approximately 2740 g / m 2 is.

[0078] The fifth flame barrier according to the present invention is obtained in the same way as the first flame barrier according to the present invention, with the only difference being that the porous fibrous nonwoven fabric has a density of approximately 2250 g / m 2 The fact is that it is made of five overlapping E-glass fibre chopped strand mats with a total area weight of 1471 kg / m². The resulting flame barrier has a thickness of 2.3 mm and a density of 1471 kg / m². 3 and the area weight is approximately 3383 g / m 2 is.

[0079] The flame-blocking properties of five flame barriers according to the present invention were tested using a Bunsen burner as shown in Figures 3a and 3b. The Bunsen burner (20) used for the test had a gas valve (21) for adjusting the gas supply and a controller for adjusting the air volume. The burner tube (22) had an inner diameter of approximately 9.5 mm and a length of approximately 90 mm. Commercially available propane was used as fuel.

[0080] For testing the first flame shield of the present invention, the Bunsen burner flame (23) was adjusted so that its temperature at the tip of the flame was approximately 1060°C before the start of the test and its temperature at the center of the flame was approximately 1040°C before the start of the test. The flame temperature at the tip of the flame was measured at a distance d = 57 mm from the end of the burner tube, while the flame temperature at the center of the flame was measured at a distance s = 35 mm from the end of the burner tube. Temperatures were measured using thermocouples. A test specimen (24) of the first flame shield of the present invention was fixed in a horizontal position in a test specimen holder (25) to expose an area approximately 250 mm x 250 mm in size. The test specimen was then positioned horizontally on top of the flame at a distance t = 60 mm from the end of the Bunsen burner tube (aligning the flame with the center of the exposed area). During the test, the flame temperature at the center of the flame was measured with a thermocouple and remained constant at 1040°C to 1050°C. Additionally, during the test, the temperature of the flame shield on the side opposite the one exposed to the flame (24) (commonly referred to as the "cover side") was also measured with a thermocouple at the center (26) of the flame shield. The test lasted for 10 minutes. The maximum temperature recorded during the test conducted at the center of the flame shield according to the present invention on the cover side was approximately 622°C. The temperature drop (the difference between the temperature at the center of the flame and the temperature at the center of the specimen on the cover side) was measured during the 10-minute test and remained constantly above approximately 422°C.

[0081] A similar procedure was followed for testing the second, third, fourth, and fifth flame shields according to the invention. The Bunsen burner flame (23) was adjusted so that its temperature at the tip of the flame before the test began was about 1080° C., and that at the center of the flame before the test began was about 1090° C. During the test, which lasted for 10 minutes, the temperature at the center of the flame was measured and remained consistently near 1090° C.

[0082] In the case of the second flame shield according to the invention, the maximum temperature recorded during the test carried out at the center of the flame shield according to the invention on the cover side was about 535° C. The temperature drop was measured during the 10 minute test and this always remained above about 555° C.

[0083] In the case of the third flame shield according to the invention, the maximum temperature recorded during the test carried out at the center of the flame shield according to the invention on the cover side was about 507° C. The temperature drop was measured during the 10 minute test and this always remained above about 583° C.

[0084] In the case of the fourth flame shield according to the invention, the maximum temperature recorded during the test carried out at the center of the flame shield according to the invention on the cover side was about 454° C. The temperature drop was measured during the 10 minute test and always remained above about 636° C.

[0085] In the case of the fifth flame shield according to the invention, the maximum temperature recorded during the test carried out in the center of the flame shield according to the invention on the cover side was about 400° C. The temperature drop was measured during the 10 minute test and always remained above about 690° C.

[0086] As can be seen from these data, all the flame barriers according to the present invention have excellent flame-blocking properties, and their thicknesses (varied between 0.8 mm and 2.3 mm) and area weights (830 g / m 2 ~3383g / m 2 Despite the small change in temperature between the fibers, the flame shield provides a temperature drop of at least 350°C over a period of at least 10 minutes. During the tests, it was observed how the polyurethane, which completely impregnates the porous fibrous nonwoven fabric to make the flame shield impermeable, forms a barrier to the flame and quickly carbonizes, forming char deposits around and on the surface of the fibers of the flame shield according to the invention. All flame shields according to the invention were able to withstand the Bunsen burner test for 10 minutes without showing any burning, softening, or dripping of the fibers and / or the polyurethane contained within the fibers. Furthermore, due to the dimensional stability ensured by the porous fibrous nonwoven fabric used, no substantial deformation of the flame shield was observed. This type of performance demonstrates how well the flame shield according to the invention is suited to mitigating the consequences of thermal runaway and protecting the vehicle interior during evacuation times.

[0087] FIG. 4 shows a housing for a battery for an electric vehicle (30) according to the present invention, together with a battery contained therein. The battery housing includes a battery cover (or battery lid) (31) and a battery tray (32). The battery consists of a number of battery cells (33). In the embodiment shown in FIG. 4, a flame shield (1) according to the present invention is applied to the battery cover on the side facing the battery, and the flame shield covers the battery cover almost entirely, even in areas with strong curvatures and beading. The possibility of such a good and safe coating is a result of the fact that both basic components of the flame shield according to the present invention have excellent design flexibility. Such a good and safe coating would be difficult, if not impossible, with prior art flame shields based on mica plates due to their tendency to cleave and / or break.

[0088] In the embodiment shown in Figure 4, the flame shield (1) according to the present invention covers only the battery cover (31). In other embodiments not shown here, the flame shield according to the present invention may be applied only on the battery tray (32), or may be applied on both the battery cover (31) and the battery tray (32).

Claims

1. 1. A flame shield (1) for batteries of electric vehicles, in particular lithium-ion batteries, characterized in that the flame shield comprises at least one flame-resistant layer made of a porous fibrous nonwoven fabric (3) impregnated with polyurethane (2), the melting temperature of the fibers contained in the porous fibrous nonwoven fabric (3) being at least 1100°C, the polyurethane not containing any flame retardant, and the polyurethane impregnating the porous fibrous nonwoven fabric such that the flame-resistant layer is impermeable to airflow.

2. 10. The flame shield for an electric vehicle battery of claim 1, wherein the at least one flame resistant layer maintains a temperature drop of at least 350°C, more preferably at least 500°C, and even more preferably at least 600°C in a Bunsen burner test lasting 5 minutes.

3. 10. The flame shield for an electric vehicle battery of claim 1, wherein the at least one flame resistant layer maintains a temperature drop of at least 350°C, more preferably at least 500°C, and even more preferably at least 600°C in a Bunsen burner test lasting 10 minutes.

4. 10. The flame shield for an electric vehicle battery of claim 1, wherein the at least one flame resistant layer maintains a temperature drop of at least 350°C, more preferably at least 500°C, and even more preferably at least 600°C in a Bunsen burner test lasting 15 minutes.

5. The flame shield according to any one of claims 1 to 4, wherein the thickness of the flame resistant layer is from 0.5 mm to 7 mm, more preferably from 0.5 mm to 5 mm, and even more preferably from 1 mm to 3 mm.

6. The density of the flame-resistant layer is 800 kg / m ３ ~1800 kg / m ３ and more preferably 1000 kg / m ３ ~1500 kg / m ３ The flame shield according to any one of claims 1 to 5,

7. The flame shield according to any one of claims 1 to 6, wherein the weight of the porous fibrous nonwoven fabric (3) is 40% to 80%, preferably 50% to 70%, of the total weight of the flame-resistant layer.

8. 8. Flame shield according to any one of claims 1 to 7, wherein the porous fibrous nonwoven (3) comprises endless filaments.

9. The flame shield according to any one of claims 1 to 8, wherein the porous fibrous nonwoven fabric (3) comprises staple fibres having a length preferably between 20 mm and 80 mm, more preferably between 30 mm and 70 mm, and even more preferably between 40 mm and 60 mm.

10. 10. A flame shield according to any one of claims 1 to 9, wherein the porous fibrous nonwoven fabric comprises fibres which are bound together by a thermosetting binder before being impregnated with a polyurethane, preferably an epoxy or phenolic binder.

11. The flame shield according to any one of claims 1 to 10, wherein the fibers of the porous fibrous nonwoven fabric (3) include at least one of ceramic fibers, glass fibers, carbon fibers, mineral fibers, and oxidized polyacrylonitrile fibers.

12. 12. Flame shield according to any one of claims 1 to 11, wherein the polyurethane (2) is obtained from the reaction of a polyurethane-forming mixture that does not contain any blowing agent.

13. A method for producing the flame shield according to any one of claims 1 to 12, comprising at least the following steps: - providing a porous fibrous nonwoven fabric, the fibers contained in said fibrous nonwoven fabric having a melting temperature of at least 1100°C; - spreading a polyurethane-forming mixture that does not contain any flame retardants onto the porous fibrous nonwoven fabric (the polyurethane mixture may be mixed and metered just before spraying; additives may be added to the mass or directly to the mixing unit); - transferring the porous fibrous nonwoven fabric spread with the polyurethane-forming mixture into a mold heated at a temperature between 40°C and 200°C, the cavity of the mold having the shape desired for the flame shield; - closing the mold and hot pressing the transferred material stack into the heated mold by keeping the mold closed under pressure with a clamping force of 100-2000 tons (the heat of the mold will (further) activate the polyurethane-forming mixture and create pressure that spreads the polyurethane around the fibers and through the pores of the porous fibrous nonwoven); - Demoulding and optionally trimming the edges A method for manufacturing a flame shield, comprising the steps of:

14. 12. A housing for a battery of an electric vehicle (30) comprising a battery cover (31) and a battery tray (32), wherein the battery cover (31) and / or the battery tray (32) comprises a flame shield according to any one of claims 1 to 11.

15. 15. A housing for a battery of an electric vehicle (30) according to claim 14, wherein the coverage of the flame shield is at least 50%, more preferably at least 60%, and even more preferably at least 70%.

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